ibm3206k0424 ETC-unknow, ibm3206k0424 Datasheet - Page 274

• Manufacturer Part Number: ibm3206k0424
• Description: Ibm Processor For Network Resources
• Manufacturer: ETC-unknow

IBM3206K0424
IBM Processor for Network Resources
Operational Description
LCD Initialization
A Logical Channel Data Structure (LCD) containing scheduling parameters for the circuit must be initialized
before segmentation can be started. The parameters that are important to the operation of this entity are:
average_interval
peak_interval
max_burst_value and
max_burst_mult
transmit_priority
drop
max_resolution
See Transmit Logical Channel Descriptor Data Structures on page 66 for further information.
A Scheduling Example
If a connection is to have an SCR of 50 Mbps and a PCR at the line rate of 150 Mbps and a MBS of 10 cells,
the LCD needs to be initialized as follows:
The following example uses a timeline to show how a connection with these parameters is scheduled. Cells
are sent every third slot while there is data to send. After the first two cells are sent there is no more data to
Transmit Buffer (CSKED)
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• average_interval = 150 Mbps/50 Mbps = 3
• peak_interval = 150 Mbps/150 Mbps = 1
• max_burst_value = 10*(3-1) = 20
This field contains the minimum average spacing allowed between cells transmitted
on this connection. It is the reciprocal of the Sustainable Cell Rate (SCR), as speci-
fied in the ATM Forum Traffic Management Specification. The value for this field is
expressed in slot times. The length of time for a slot is defined by the Timeslot
Prescaler Register and should normally be set to one cell time.
This field contains the minimum spacing allowed between consecutive cells on this
connection. It is the reciprocal of the Peak Cell Rate as specified in the ATM Forum
Traffic Management Specification. This spacing is also expressed in slot times. A
connection that can transmit every slot time would have a value of ‘1’ for this field.
The values in these fields are used to limit the number of cells that can be trans-
ferred at the peak rate. The max_burst_value will be multiplied by four to the power
of the max_burst_mult to yield the maximum credit time. This time is expressed in
slot times and represents the time it would take to acquire the maximum number of
cell credits. This maximum credit time should equal the average interval minus the
peak interval, multiplied by the maximum number of cells (MBS) that can be trans-
ferred at the peak rate.
This field specifies the priority of transmission on this connection. Three levels of
priority are available. Connections needing the highest quality of service, such as a
CBR connection, should use the highest priority. Connections with the lowest
quality of service requirements, such as a UBR connection, should use the lowest
priority.
Data can be sent on up to four physical drops. This field specifies the drop for this
connection.
If this bit is set, the lower eight bits of the average interval and peak interval param-
eters contain a fractional component. This allows a finer resolution for scheduling.
For example, for a peak interval of 1.5 time units, the value written to the
peak_interval field should be hex 0180. If this bit is set, the initial value of time-
stamp should contain the current timeslot counter shifted 16 bits to the left.
pnr25.chapt05.01
August 14, 2000
Preliminary